The present invention relates to a gas turbine and more particularly to a gas turbine formed so that a part of high-pressure air compressed by a gas turbine compressor is used as air for a cooling air system and a spray air system.
As countermeasures for a recent increase in demands of power and global warming, realization of large capacity and high efficiency of gas turbine power generating equipment is required. Particularly, in gas turbine power generating equipment leading air compressed by a compressor to a combustor, supplying fuel to burn it with the air, and driving the gas turbine by its combustion gas, large capacity and high efficiency can be realized by increasing the combustion temperature more.
However, in a heat recovery type gas turbine, that is, a gas turbine for recovering energy held by higher-temperature combustion gas, there is the possibility that damage may be caused to parts exposed at a high temperature without cooling and developed to a serious accident. Therefore, in gas turbine power generating equipment in which a combustion gas temperature is high, the high-temperature part of the gas turbine is cooled using compressed air or vapor as a cooling medium.
On the other hand, when oil such as light oil is to be used as fuel, spray air for spraying fuel into a combustor is necessary. A conventional spray air system adjusts the air temperature by a heat exchanger using a part of air discharged from a compressor, pressurizes it by the compressor to air of higher pressure than air for combustion, produces clean air by letting it pass through a filter so as to prevent the fuel nozzle from clogging, then supplies air to the combustor and uses it to spray fuel.
A conventional cooling air system supplies air extracted by the compressor to the high-temperature part of the turbine directly or after it passes through the heat exchanger for temperature adjustment. In this case, in a gas turbine which uses a part of air discharged from the compressor for cooling the turbine blades so as to improve the turbine efficiency and then recovers it into the combustor, a heat exchanger for keeping cooling air at an appropriate temperature and a filter and a mist separator for making cooling air more clean are installed.
A system constitution for cooling air discharged from the compressor by the heat exchanger, cooling the high-temperature part of the turbine, and also using it as fuel spray air, is disclosed, for example, in Japanese Patent Application Laid-Open 4-214931 and its equivalent, Nishijima U.S. Pat. No. 5,185,997.
In a gas turbine formed as mentioned above, that is, a gas turbine having a fuel oil spray air system and a cooling air system in common and formed so that a boost compressor is driven by the turbine shaft from the viewpoint of reliability of cooling air supply, the number of revolutions of the turbine at start is small, so that the discharge pressure of the boost compressor is insufficient and hence at start, an air system for compensating for it is necessary.